Polyesters have been produced commercially on a large scale for processing into shaped articles such as fibers, films and bottles, primarily from poly(ethylene terephthalate). Synthetic polyester yarns, for example, have been known and used commercially for several decades, having been first suggested by W. H. Carothers, U.S. Pat. No. 2,071,251, and then Whinfield and Dickson suggested poly(ethylene terephthalate) in U.S. Pat. No. 2,465,319. This polyester polymer has been used most frequently for commercial purposes and has been made from ethylene glycol and from dimethyl terephthalate or terephthalic acid; these polymer precursors have been conveniently reacted together commercially by ester interchange or by direct esterification, respectively, followed by condensation polymerization, generally in multiple stages, with appropriate provision to remove condensation products, such as water, and also excess ethylene glycol that is preferably recycled with removal of unwanted water and by-products, as appropriate, as described in the art, e.g., Edging and Lee, U.S. Pat. No. 4,110,316, MacLean and Estes, U.S. Pat. No. 4,113,704, Goodley and Shiffier, U.S. Pat. No. 4,146,729, and Goodley and Taylor, U.S. Pat. No. 4,945,151.
Originally, polyester yarns were made by batch operations, involving several separate processes, first making the polyester polymer, and then melt-spinning the polymer into filaments, and further processing the filaments into continuous filament yarns or staple fiber, as described, e.g., by Ludewig in "Polyester Fibres, Chemistry and Technology", first published in German in 1964, and then in an English translation by John Wiley & Sons Ltd., 1971. However, as indicated in the literature, there has always been a desire to economize, and so to couple various separate stages together. Some fiber manufacturers have operated a wholly continuous process, starting with the polymer precursors that are reacted together and then polymerized to form a polyester polymer melt that is extruded into solid filaments that are processed into continuous (multi-filament) yarns as a wholly continuous process, or into staple fiber (usually as a separate process). However, many manufacturers, in various countries, have not changed to a continuous process, because of the problems presented by continuous operations.
As indicated, although many polyester polymers (including copolymers) have been suggested, the polyester most widely manufactured and used hitherto for textile fibers has been poly(ethylene terephthalate), which is often referred to as homopolymer. Homopolymer has generally been preferred over copolymers because of its lower cost, and also because its properties have been entirely adequate, or even preferred, for most end-uses. It is known, however, that homopolymer requires special dyeing conditions (high temperature requiring super-atmospheric pressure) not required for nylon fibers, for example. Homopolymer is often referred to as 2G-T.
Poly(ethylene terephthalate/5-sodium-sulfoisophthalate) copolyester has, however, also been manufactured and used commercially in considerable quantities for some thirty years, especially for staple. This copolyester was first suggested by Griffing and Remington in U.S. Pat. No. 3,018,272. A very desirable feature of this copolyester is its affinity for basic (cationic) dyes. Commercially, such copolyester has contained about 2 mole % of the ethylene 5-sodium-sulfo-isophthalate repeat units. Such basic-dyeable copolyester has sometimes been referred to as 2G-T/SSI. This basic-dyeable copolyester has been regarded as important. It has long been highly desirable to make improvements in providing basic-dyeable copolyesters, especially for spinning into filaments for use as textile fibers.
As indicated in the literature, e.g., Chapter 4 of Ludewig's authoritative book, especially page 100, antimony trioxide (Sb.sub.2 O.sub.3) has been "frequently mentioned in the literature and is in a class of its own" as a polymerization catalyst. When one reads the patent literature, most working Examples have used antimony trioxide as polymerization catalyst; e.g., nearly all Griffing and Remington's Examples used antimony trioxide; only Examples 13 and 18 did not use an antimony trioxide polymerization catalyst, but used tetraisopropyltitanate instead. We believe that antimony trioxide is far and away the predominant material that has been added for use as polymerization catalyst in actual commercial practice although there have been many complaints in the literature about disadvantages resulting from its use, and despite many suggestions for avoiding its use; e.g., WO 93/22367 (Mueller, Rhone-Poulenc Viscosuisse) suggests using a mixed catalyst consisting of 10 to 75 ppm of lithium and 15 to 80 ppm of germanium (which latter was already known as a useful catalyst). To summarize this aspect, an antimony polymerization catalyst is still believed to be used in commercial operations virtually exclusively, despite its well-known disadvantages, and it has long been known to be desirable to find a way to avoid such disadvantages.
As indicated in the literature, such as Chapter 4 of Ludewig, especially page 105, titanium dioxide (TiO.sub.2) is a preferred delustering agent used for polyester fiber. So most commercial fiber is now delustered with titanium dioxide: amounts of 1-2% by weight have been used to make what is often referred to as "dull" fiber; amounts of 0.2-0.5% by weight of titanium dioxide have been used to make what is often referred to as "semi-dull" fiber; some "clear polymer" without any delustering agent is also used to make polyester fibers.
The present invention provides a novel process for preparing sulfonate-modified (basic-dyeable) polyesters of the type originally invented by Griffing and Remington with surprising advantages, especially in avoiding the prior art's reliance on adding an antimony catalyst in the condensation polymerization, and leading to new compositions of matter with improvements in processing and products.